Cellulose acetate fibers are used as absorbers for hygienic goods such as a disposable diaper and sanitary product other than a tobacco filter material. Crimp is applied to a tow of the cellulose acetate filaments, in order to give a swelling to a thread and to make a spinning work easy.
The crimped filaments are transported in a state of being packed in a bale form and being degassed and compressed in a cubical packing container.
In addition, at the time of manufacturing of a final product, after taking out filaments from the bale, the filaments are opened and then molded into a desired shape.
In Patent Document 1 (JP-B 61-7824), the absorber for hygienic goods, made of cellulose acetate fibers is disclosed.
In the above-mentioned Patent Document 1, it is described that one obtained by opening a tow of crimped long-sized fibers of cellulose acetate or one obtained by making short fibers into web has a relatively large water absorption and retention capacity.
In Patent Document 2 (U.S. Pat. No. 3,282,768) and Patent Document 3 (U.S. Pat. No. 3,099,594), there is described an opening method by using air-jet in order to reduce and prevent the damage which is given to a tow by the conventional machine opening.
Furthermore, in Patent Document 4 (U.S. Pat. No. 3,297,506), there is proposed an air opening apparatus which can solve the problems of Patent Documents 2 and 3.
In Patent Document 5 (JP-A 59-500422), there is disclosed an invention where opening is done in a sheet shape by using air opening.
In Patent Document 6 (JP-A 2004-244794), there is disclosed a method for making an absorbent composite by spreading a crimped tow in the direction perpendicular to the direction of tow movement, de-registering the crimped tow, shaping the de-registered tow to a substantially rectangular cross-section, and dispersing a particulate onto the entire shaped tow.
In Patent Document 6, there is further described, in preparation of a diaper which contains a high water-absorbable resin (super absorbent polymer) (super-absorbable polymer in Patent Document 2) (SAP), the SAP powder or slurry is distributed downward to the air-opened tow in the vertical direction, and then is fed to rollers.
In Patent Document 7 (U.S. Pat. No. 3,262,181), there is disclosed a process including introducing the crimped tow into a processing zone in a substantially unidirectional path, directing, in substantially the same direction as the movement to the tow, a first stream of motivating gas, downstream from the introduction of the first motivating gas directing a separate stream of motivating gas against the tow also substantially in the direction of movement of the tow, and, by the separate stream, opening the previously crimped filaments of the tow and, furthermore, performing compression into a unitary rod-like structure.
In Patent Document 8 (JP-A 2008-255529), there are disclosed a fibrous sheet excellent in absorbability over liquids such as water, and a method and an apparatus for manufacturing the fibrous sheet simply.
In each of the above-mentioned prior art documents, the water-absorbent resin (SAP) is added to the fibrous sheet after opening a tow. The reason is because it has been considered conventionally that since a tow bundle in a state where opening has not yet finished is not bulky, the SPA cannot enter the tow bundle even when scattering an additive.
For this reason, as is mentioned in the above-mentioned prior art documents in which the SAP is added to the fibrous sheet after opening a tow, the SAP is mostly unevenly distributed on one surface (upper surface) in the thickness direction of the tow, and there arises a problem when used as an absorber.
Fall-off of the SAP may arise after the subsequent processing.
Although a solution of the problem resulting from the uneven distribution of such SAP is also examined, and for example, the method for obtaining an thin absorbent having a low basis weight is disclosed in Patent Document 9 (JP-A 2006-102479), the method is very complicated.
When employing an opening matter of a tow as manufacture materials of absorbers for hygienic goods such as a disposable diaper, a wide-shaped material is easily processed.
However, according to the prior arts, it is difficult to manufacture a wide-shaped material being suitable for the above-mentioned uses, and when a wide-shaped tow opening matter is forcibly manufactured, it is considered that the following new problems are caused.
When a wide-shaped tow opening matter is manufactured from a tow having the same mass, a density of the tow opening matter becomes small. For this reason, when the SAP is sprayed to the tow opening matter by utilizing pneumatic pressure, there is a possibility that a problem of blowing off of the SAP through the spaces may be caused without holding SAP by a tow opening matter.
Instead of the above-mentioned opening, although a wide-shaped material can be obtained by collapsing the obtained tow opening matter having a circular cross-sectional shape with molding rollers or the like, in such a case, there are problems in which there is only obtained a material in which a thickness is large and a density is large in the center portion, and a thickness is small and a density is small in the both side portions, and thus the absorption performance is deteriorated easily.